This invention relates to the field of integrated circuit (IC) design. Specifically, it relates to an integrated circuit having a low-voltage, low-power band-gap reference circuit for outputting a reference parameter and a low-voltage, low-power temperature sensor circuit for sensing the on-chip temperature of a semiconductor chip using at least the reference parameter.
Semiconductor memory units embedded within an integrated circuit (IC) system are arranged in arrays of cells, where each cell stores one bit of information (1 or 0). Generally, in order to maintain the integrity of the data stored within an embedded semiconductor memory unit, such as an embedded dynamic random access memory unit (eDRAM), each cell of the memory unit requires periodic refreshing, since a small charge stored in each cell of the memory unit tends to leak off due to several factors, such as an increase in the temperature of the chip. Accordingly, circuitry is required to manage or control such semiconductor memory units for refreshing the cells. Hence, these circuits consume power causing a reduction in the lifetime of the battery when these circuits are utilized in hand-held, battery-operated devices.
For instance, the refresh circuitry generally includes several charge circuits which need to be activated to provide different voltage and current supplies to cells and other circuits of the memory unit. These charge circuits consume power which can significantly reduce battery lifetime. Additionally, the consumption of power by these charge circuits causes the chip temperature to increase, thereby decreasing the period of time between refresh cycles of the charge circuits. This further causes a reduction in the battery lifetime, since the charge circuits are activated at a greater frequency.
Furthermore, a respective constant-speed ring oscillator provided in proximity or within the memory unit is generally used to run these charge circuits. A typical frequency range for the oscillator is from 5 MHZ to 50 MHZ depending on the voltage or current required to be produced by the particular charge circuit. Hence, additional power is required to operate the constant-speed ring oscillators.
Since the charge circuits consume a relatively large amount of power, memory units are generally designed with a few or no additional circuits for adding additional features to the memory unit, such as band-gap reference circuit for providing a band-gap reference voltage, and a temperature sensor circuit for approximating the chip temperature. Further, when these additional circuits are added to the memory unit, they not only consume a great amount of power, but, as a consequence of consuming a great amount of power, they further facilitate the increase in the chip temperature. As indicated above, an increase in the chip temperature causes a decrease in the period of time between refresh cycles of the charge circuits, thereby causing the charge circuits to be activated at a greater frequency and consequently, draining the battery at a more rapid rate.
Further, these additional circuits are generally not designed to operate during low-power applications, especially when the supply voltage drops under one volt (a xe2x80x9csub-one voltagexe2x80x9d), such that these circuits may be insensitive to the supply voltage. A paper published by Toshiba, Inc. in the IEEE Journal of Solid State Circuits, vol. 34, no. 5, page 670, May 1999, proposes a circuit to produce a CMOS band-gap reference voltage (Vref), where the circuit is capable of operating with a sub-one volt supply voltage. The paper discusses combining two current flows, one having a positive temperature coefficient and one having a negative temperature coefficient, and converting them to a reference voltage. However, the paper does not teach or discuss how to operate the proposed circuit in a low-power mode.
An objective of the present invention is to provide a band-gap reference for providing a reference parameter, such as a constant reference voltage, for a semiconductor chip, such as a memory, microprocessor, or logic, where the band-gap reference circuit can be operated at low-voltage and low-power, and is insensitive to supply voltage, variation of fabrication process, and chip temperature.
Another objective of the present invention is to provide an on-chip temperature sensor circuit using the whole or part of the low-power, low-voltage band-gap reference circuit. The temperature sensor circuit can be used to monitor chip temperature for many different purposes, such as control refresh cycle time of DRAM array, adjust clock rate of a microprocessor chip, etc.
Further, another objective of the present invention is to provide a combined low-voltage, low-power band-gap reference and temperature sensor circuit for providing a band-gap reference parameter and for sensing the temperature of a chip, such as an eDRAM memory unit or CPU chip, using the band-gap reference parameter. The combined sensor circuit is insensitive to supply voltage and a variation in the chip temperature. The power consumption of both circuits encompassing the combined sensor circuit is less than one xcexcW. The combined sensor circuit can be used to monitor local or global chip temperature. The result can be used to (1) regulate DRAM array refresh cycle time, e.g., the higher the temperature, the shorter the refresh cycle time, (2) to activate an on-chip or off-chip cooling or heating device to regulate the chip temperature, (3) to adjust internally generated voltage level, and (4) to adjust the CPU (or microprocessor) clock rate, i.e., frequency, so that the chip will not overheat.
Still, another objective of the present invention is to implement the band-gap reference and temperature sensor circuit having low-power circuits within a battery-operated device having at least one memory unit. The low-power circuits extend battery lifetime and data retention time of the cells of the at least one memory unit.